<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <HTML> <HEAD> <META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9"> <TITLE>VoIP Howto: Communications using PSTN line</TITLE> <LINK HREF="VoIP-HOWTO-9.html" REL=next> <LINK HREF="VoIP-HOWTO-7.html" REL=previous> <LINK HREF="VoIP-HOWTO.html#toc8" REL=contents> </HEAD> <BODY> <A HREF="VoIP-HOWTO-9.html">Next</A> <A HREF="VoIP-HOWTO-7.html">Previous</A> <A HREF="VoIP-HOWTO.html#toc8">Contents</A> <HR> <H2><A NAME="s8">8. Communications using PSTN line</A></H2> <H2><A NAME="ss8.1">8.1 Overview</A> </H2> <P>VoIP becomes very interesting when you start to use PSTN lines to call other people in the world, directly to their home telephone. <H2><A NAME="ss8.2">8.2 Scenario</A> </H2> <P>A typical application is like that: <P> <PRE> Home telephone1 -- (PSTN) -- PC1 -- (Internet) -- PC2 -- (PSTN) -- Home telephone2 </PRE> <P> <OL> <LI>Home Telephone1 make a calls to PC1 phone number (using PSTN line, I mean classic telephone line).</LI> <LI>PC1 answer to it.</LI> <LI>Home telephone1 must tell PC1 what gateway use (PC2 in this case) by giving the IP address (from DTMF keyboard) and/or what number call (in this case Home telephone2).</LI> <LI>After that PC1 will start to make an H323 call to PC2, then it will pass Home telephone2 to PC2 to make it call it throught PSTN line.</LI> <LI>Home telephone2 answers to call and communication between Home telephone1 and Home telephone2 begins.</LI> </OL> <H2><A NAME="ss8.3">8.3 What can be changed in this configuration? </A> </H2> <P> <OL> <LI>You may use a PBX to select many lines to access many PC1 gateway (for example one to call within your state, one to go accross Europe, and so on...): typically you don't have to change this, cause cost is always the same.</LI> <LI>You can select (after called your PC1 gateway) every PC2 you want (for example a PC2 living in England to call an English person so that you'd pay only intra-country costs).</LI> </OL> <P>So your decision will be taken considering PSTN line costs. In fact what VoIP does is the convert this: <P> <PRE> Home Telephone1 --- (PSTN) --- Home Telephone2 PSTN great distance calling cost </PRE> <P>into this: <P> <PRE> Home Telephone1 --- (PSTN) --- PC1 + PC2 ---- (PSTN) --- Home Telephone2 = -------------------------------------- 2 PSTN short distance calling costs </PRE> <P>To save money you need that: <P> <PRE> 2 PSTN short distance calling costs < PSTN great distance calling cost </PRE> <P>Typically "short distance calling" refers to a "city cal" while "great distance calling" can be an "intercontinental call"! <HR> <A HREF="VoIP-HOWTO-9.html">Next</A> <A HREF="VoIP-HOWTO-7.html">Previous</A> <A HREF="VoIP-HOWTO.html#toc8">Contents</A> </BODY> </HTML>